05 Suburban Z71 rear caliper carrier removal?

I have a warped rotor on the back and have the parts to replace it. I tore into it last weekend and got the caliper off and pads removed then the problems started. I was ready for a Torx bit bolt but it looked to be a 17mm bolt head. I got the 17mm socket but it wouldn't fit the head so I got 18 and it was to big. My friend gets a 11/16 and it doesn't fit either.

Sounds like it's been rounded out, or like Pikey said it's all crudded up. I bought a set of rounded bolt sockets from harbor freight for $20.00, and they have saved me more than once. As a matter of fact I just had to use the 10mm, to remove a stripped bleeder screw out of a caliper.

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From the factory they come with a T65 torx bit for the caliper bolts, but most people replace them with the hex head style bolts to avoid problems down the road. Auto Zone has them for $4.99 each, just replaced all of my last summer.